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Title: Transformations of Mercury, Iron, And Sulfur During the Reductive Dissolution of Iron Oxyhydroxide By Sulfide

Abstract

No abstract prepared.

Authors:
; ; ;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
901000
Report Number(s):
SLAC-REPRINT-2006-212
Journal ID: ISSN 0016-7037; GCACAK; TRN: US200713%%257
DOE Contract Number:
AC02-76SF00515
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geochim.Cosmochim.Acta 71:877-894,2006; Journal Volume: 71
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; REDUCTION; DISSOLUTION; IRON; MERCURY; SULFIDES; SULFUR; PHASE TRANSFORMATIONS; HYDROXIDES; IRON COMPOUNDS; Other,OTHER

Citation Formats

Slowey, A.J., /Stanford U., Geo. Environ. Sci., Brown, G.E., and /SLAC, SSRL. Transformations of Mercury, Iron, And Sulfur During the Reductive Dissolution of Iron Oxyhydroxide By Sulfide. United States: N. p., 2007. Web. doi:10.1016/j.gca.2006.11.011.
Slowey, A.J., /Stanford U., Geo. Environ. Sci., Brown, G.E., & /SLAC, SSRL. Transformations of Mercury, Iron, And Sulfur During the Reductive Dissolution of Iron Oxyhydroxide By Sulfide. United States. doi:10.1016/j.gca.2006.11.011.
Slowey, A.J., /Stanford U., Geo. Environ. Sci., Brown, G.E., and /SLAC, SSRL. Wed . "Transformations of Mercury, Iron, And Sulfur During the Reductive Dissolution of Iron Oxyhydroxide By Sulfide". United States. doi:10.1016/j.gca.2006.11.011.
@article{osti_901000,
title = {Transformations of Mercury, Iron, And Sulfur During the Reductive Dissolution of Iron Oxyhydroxide By Sulfide},
author = {Slowey, A.J. and /Stanford U., Geo. Environ. Sci. and Brown, G.E. and /SLAC, SSRL},
abstractNote = {No abstract prepared.},
doi = {10.1016/j.gca.2006.11.011},
journal = {Geochim.Cosmochim.Acta 71:877-894,2006},
number = ,
volume = 71,
place = {United States},
year = {Wed Mar 14 00:00:00 EDT 2007},
month = {Wed Mar 14 00:00:00 EDT 2007}
}
  • This experimental study investigated the processes by which microbes interact with oxyhydroxide mineral surface coatings using an approach designed to better represent the conditions of natural subsurface environments. The interactions of Shewanella putrefaciens, a facultative anaerobe capable of dissimilatory iron reduction, with coatings of Fe{sup 3+} and Al{sup 3+} oxyhydroxides on natural quartz and silica glass surfaces were examined. Using synthetic groundwater solutions having composition that simulated a typical aquifer, bacteria were seeded onto mineral surfaces (and coatings) and incubated in parallel with abiotic controls for up to 96 h under aerobic and anaerobic conditions. Microbial-mineral surface interactions were determinedmore » using the direct observational technique, Fluid Tapping Mode{trademark} Atomic Force Microscopy (TMAFM) in combination with measurements of ferrous iron concentrations and pH of the incubating solutions. Observations of live bacteria-surface interactions exposed to aerobic conditions showed localized pitting on Fe{sup 3+} oxyhydroxide coated quartz surfaces within 72 h of incubation. These pits corresponded directly to sites of bacterial surface adhesion and the extent of pitting was accompanied by the accumulation of ferrous iron to low but steady-state concentrations. Localized pitting was not observed on any Al{sup 3+} oxyhydroxide coated surfaces. In contrast, iron coated surfaces exposed to bacteria under anaerobic conditions revealed progressive, nonlocalized Fe loss over 96 h. This correlated with a temporal increase in ferrous iron concentrations in the bacteria-exposed solutions compared to the abiotic controls. Aqueous chemical measurements combined with the Fluid TMAFM observations indicate biologically-catalyzed iron reduction under both aerobic and anaerobic incubation. 57 refs., 7 figs.« less
  • No abstract prepared.
  • Mercury (Hg) is a toxic heavy metal that poses significant environmental and human health risks. Soils and sediments, where Hg can exist as the Hg sulfide mineral metacinnabar (β-HgS), represent major Hg reservoirs in aquatic environments. Metacinnabar has historically been considered a sink for Hg in all but severely acidic environments, and thus disregarded as a potential source of Hg back to aqueous or gaseous pools. In this study, we conducted a combination of field and laboratory incubations to identify the potential for metacinnabar as a source of dissolved Hg within near neutral pH environments and the underpinning (a)biotic mechanismsmore » at play. We show that the abundant and widespread sulfur-oxidizing bacteria of the genus Thiobacillus extensively colonized metacinnabar chips incubated within aerobic, near neutral pH creek sediments. Laboratory incubations of axenic Thiobacillus thioparus cultures led to the release of metacinnabar-hosted Hg(II) and subsequent volatilization to Hg(0). This dissolution and volatilization was greatly enhanced in the presence of thiosulfate, which served a dual role by enhancing HgS dissolution through Hg complexation and providing an additional metabolic substrate for Thiobacillus. These findings reveal a new coupled abiotic-biotic pathway for the transformation of metacinnabar-bound Hg(II) to Hg(0), while expanding the sulfide substrates available for neutrophilic chemosynthetic bacteria to Hg-laden sulfides. Lastly, they also point to mineral-hosted Hg as an underappreciated source of gaseous elemental Hg to the environment.« less
  • No abstract prepared.
  • There is growing awareness of the complexity of potential reaction pathways and the associated solid-phase transformations during the reduction of Fe (hydr)oxides, especially ferrihydrite. An important observation in static and advective-dominated systems is that microbially produced Fe(II) accelerates Ostwald ripening of ferrihydrite, thus promoting the formation of thermodynamically more stable ferric phases (lepidocrocite and goethite) and, at higher Fe(II) surface loadings, the precipitation of magnetite; high Fe(II) levels can also lead to green rust formation, and with high carbonate levels siderite may also be formed. This study expands this emerging conceptual model to a diffusion-dominated system that mimics an idealizedmore » micropore of a ferrihydrite-coated soil aggregate undergoing reduction. Using a novel diffusion cell, coupled with micro-x-ray fluorescence and absorption spectroscopies, we determined that diffusion-controlled gradients in Fe{sup 2+}{sub (aq)} result in a complex array of spatially distributed secondary mineral phases. At the diffusive pore entrance, where Fe{sup 2+} concentrations are highest, green rust and magnetite are the dominant secondary Fe (hydr)oxides (30 mol% Fe each). At intermediate distances from the inlet, green rust is not observed and the proportion of magnetite decreases from approximately 30 to <10%. Across this same transect, the proportion of goethite increases from undetectable up to >50%. At greater distances from the advective-diffusive boundary, goethite is the dominant phase, comprising between 40 and 95% of the Fe. In the presence of magnetite, lepidocrocite forms as a transient-intermediate phase during ferrihydrite-to-goethite conversion; in the absence of magnetite, conversion to goethite is more limited. These experimental observations, coupled with results of reactive transport modeling, confirm the conceptual model and illustrate the potential importance of diffusion-generated concentration gradients in dissolved Fe{sup 2+} on the fate of ferrihydrite during reduction in structured soils.« less